OP, I have no idea, if this accident caused diminished value. But I can suggest the following course of action, if you feel it has.
1) commercial trucking, insurance companies, are by default very hard to deal with
2) you have not yet, got their attention. they tend to deny, deny and deny, it is what they do.
3) You do not need to hire an attorney, because first you would have a very difficult time finding one to take it, on a contingent basis.
4) If it were me, I would hire and attorney to write a letter, with your demands. That should be $300ish
5) The magic words, that will get their attention are ( you feel they are negotiating in bad faith). And if they do not respond, you will file a complaint, with the insurance commissioner (OIC) and the attorney general.
6) that should get their attention, and you may find them more willing to talk.
7) the bad faith thing is "the big hammer" last thing they want is the OIC, calling them up and investigating them.
This of course, is only my opinion. But it is based on my 40 years of treating patients involved in MVA's. And that, two of my daughters are attorneys. So take it for what you feel it is worth. Maybe something, maybe nothing